Apparatus and method for bending and straightening curved printing plates and the like



May 25, 1954 J. SC APPARATUS AND METHOD Filed May 23, 1952 HWARTZ ET ALFOR BENDING AND STRAIGHTENING CURVED PRINTIHG PLATES AND THE LIKE 2Sheets-Shea T. l

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INVENTORS: Josgph ScfiWariz &.

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A TTORNEYS.

9 7 9 7 2 G N I N E T w um RI L .sE LD m M T m EMA I S n m Rum M G H m CT s m R J P May 25, 1954 APPARATUS AND METHOD F0 CURVED 2 Sheets-Sheet 2Filed May 25, 1952 INVENTORS: Jase Scilwdrgz &

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ATTORNEYS.

Patented May 25, 1954 STATES ATEN-T OFF-1GB tion of PennsylvaniaApplication-Mayra 1952, Serial No. 289,511

4 Claims.-

1.; This-inventionrelatesto an apparatus and method for modifying theshapehf acurved plate; and-more specifically relates to apparatus andmethod for holding-a curvedprinting plateand carrying out surfaceshaping and restoring operations thereon;

Curved printing plates are usedextensively in connection withautoma-tieprinting machines which embodya cylinder or other roundedmemher to which the-curved printing plate may be attached. a Theetchedor printing surface of the I curved plate faces outwardly. and isadapted automatically to contact the successive sheets of paper uponwhich the printed matteristo be impressed; For proper automaticoperation of the machine, .and particularly. for uniform andaecuratereproductionof the printed matter, it is' -essential that the printing.face of the printingplate be absolutely uniform; that is, the surfacemust be uniformly curved and free or high spots or low spots which willtend either to printtooboldly. or too lightly in local portions of thetotal printed area.

In the course of preparation of such printing plates, they arefrequently handled. or processed insuch manner that low spots tend todevelop on 1 the printed surface, and it is-accordinglyone ob-' ject ofthis invention to provide economical, rapid and accurate method andmeans for-eliminating localized low spots from a-curved printing plate.Other objects and advantages of the invention, including the simplicityand economyof the same, the accuracy and speed with which it may bepracticed, and the ease of adjustability-of the device for accommodationof Work objects of different sizes and diametera will appear infurtherdetail hereinafter and in the drawings, whereof:

Fig. 1 is-a perspective view of the apparatus comprising one embodimentof the invention, showing, in full line, .a movable clamp elementininoperative position withdrawn from the work;

Fig. 2 is an enlarged fragmentary sectional view takelr =as indicated bythe lines and arrows II -II which appear in Fig. 1;

Fig. 3 is an enlarged fragmentary sectional view taken as indicated bythe lines and arrows III--III which appear in Fig. 1, with parts brokenaway.

and shown in section in order more clearly to disclose importantdetails;

Fig. 4 is asectional view-taken as indicated by-the lines and arrowsIV-IV in Fig. 1, showing .theclamp' element in operative positionrelative to the work;

Figs. 5', 6 and 7' show- Qneprocedureior fiattem' ced-ure in accordancewith this" invention, -and-= the product attained inaccordance withsuch: procedure;

In the-following detailed description which relates to one specificembcdiment of-this invention as shown in the-drawings, specific termswill "be-employed for: the sake of clarity, but it is to*be-unole'rstood that suchterms are useda descriptive sense'and are notintended to-limitthe scope -of the invention-.--

Referring to the drawings, the device thereshown includes a concave slabH having a co'n--- cave upper face I Z-the shape of whichconforms;substantiallyto-the shape of the lower'face of a work object i3, hereillustrated-as a printing plate which may consist of relatively soft,man ieable/metal. The face I2 ofconcaveslab H and the face ofthe workobiect l3 both have the: shape of-a portion of a cylinder. However, duetonon-uniformity of the work objects 13, they do not neoessarilyifitsnugly. against-the concave upper face lief concave-slab ll.-

Fixed tooneend of concave slab H, at oppo sitesides thereof, are .a pairof-curved ratchet bars: l 4 =which extend Aupwardly. beyond the end- 4of concave slab 1 l. The curved upper surface of i each ratchet bar-Mds'flushwith the concave upper face l2. Transverse brace rods l5 serveto. maintain the parallel :relation'shipof ratcheo barslik. Slidablymounted on each ratchet'bar i 4' isa. rider carriage 6 Y which has.upper flanges I? in contact with the upper surface of the: ratchet bar:I l. A crossbar-264s afiixed to, and bridges the space between, .the'rider carriages E5. The: bottomface or" crossbar 20 has the". samecurvature as the top. faces-101 the'ratchet bars i4. Cross-bar 23-hasca-pacity to be swung inwardly and outwardly; through the arcdefinedby the curvature-of the ratchet' bars l4,.and: to move immediatelyadjacentthe upper-face-H of concave slab l i to an operative positionagainst an end'of work objcct l3, as indicatedin dotdash lines in Fig.11

The rider carriagels, see particularly. Fig. 2'

of the drawings, includes side wall'fil which sustains a' transverse"pivot pin 22. Rotatably 3 headed screw 2! slidably extends. Screw 21 isfixed in side wall 21 and serves to retain the pawl 23 against the sidewall 2i and as a limit stop for the rotary movement of the pawl 23around pivot pin 22.

Fixed to the opposite end of concave slab ll, opposite the ridercarriages it, are three screw clamp elements comprehensively designatedby the number 30. Referring particularly to Fig. 3 of the drawings, arigid base 3i is affixed to to the end of the concave slab ll andprovided with threaded apertures for reception of the threaded shafts32. The upper side of rigid base 3| is flush with the upper face l2 ofconcave slab ll. Each threaded shaft 32 extends through an aperture inthe base of a channel iron 33 having a lower wing 34 and an upper wing35 longer than lower wing 34. The upper wing 35 normally extends beyondthe fixed base 3| and contacts the upper face l2 of concave slab ii. Theend of upper wing 35 is constructed and arranged to contact the adjacentend of work object I3. Fixed to the threaded shaft 32 is a head 36 withhandle members 37, whereby the threaded shaft 32 may be rotated manuallyto clamp the work object it in place. A coil spring 40, normally undercompression, is fitted at one end under the head 35 and at the other endin a recess at the base of channel iron 33.

In operation, the presence and location of low spots on printing platesis determined by rubbing a fiat piece of chalk or the like on the bottomface of the printing plate, which is the etched or printing face of theplate. The chalk adheres substantially uniformly to the true portions ofthis face, but no chalk rubs off on the printing face portion of the lowspot. The opposite face of the printing plate may then be marked to showthe locations of all low spots found.

The work object l3 thus marked is placed, with the marked side up, onthe concave slab H with one end substantially in contact with the upperwings 35 of screw clamp elements 36. The rider carriages l6 togetherwith cross bar 20 are then swung downwardly and inwardly toward the workobject 13, along the ratchet bars it which serve as tracks, to theposition shown in dot-dash lines in Fig. l. The pawls 23 and ratchetbars 14 coact to maintain the.

inner edge of cross bar 20 against the adjacent end of work object l3.The work object I3 is thereby maintained between the clamp elementsadjacent its opposite ends, with relatively light pressure exerted onsaid ends. The operator now turns the threaded shafts 32, forcing theupper wings 35 under relatively great pressure against the work object,the pressure being resisted by the pawls 23 and ratchet bars [4 at theopposite end. of the work object iii. The opposed forces A thus appliedto the opposite ends of the concave work object l3 have downwardlydirected components B which expand the work object 13 under pressureagainst the upper face l2 of concave slab II, as indicated in Fig. 4 ofthe drawings. Thus the work object i3 is in uniform intimate contactthroughout its length with the concave slab II.

The work object, held under pressure in this manner, is preferablyprocessed as indicated in Figs. 8-10 of the drawings, wherein theoperator hammers downwardly upon the low spots 45, which do not contactthe upper face l2 of concave slab ll. It will be appreciated that the 4portion 41 is shown greatly enlarged in the drawings.

After concluding the hammering operation, the screw clamp elements 3dare loosened or the pawl handles 24 manipulated permitting the removalof the uniformly curved printing plate which is free of low spots, asshown in Fig. 10, from the concave slab II.

We have found that it is of vital importance to force the printing plateunder relatively high pressure against the concave slab, in order toattain proper results. Referring to Figs. the printing plate i3 is noturged against the concave slab H with suflicient force to maintain theopposed surfaces in intimate contact with one another; the printingplate bridges across the concave slab. Accordingly a hammer blow,directed against the low spot 4| of Fig. 5, often fails to correct theshape of the work spot and, on the contrary, produces a high spot 42,see Fig. 6, since the momentum of the hammer is not opposed by theconcave slab H at the precise point where the hammer is applied to theprinting plate. A high spot of the character thus produced cannotproperly be repaired by hammering on the opposite, or lower face of theprinting plate since the etching or print which appears on this lowerface is readily distorted or obliterated by hammering directly thereon.A plate as shown in Fig. '1, having a high spot 42, does not performproperly in an automatic printing press and produces a non-uniformprinted product.

Not only does our apparatus eliminate the formation of high spots asindicated in Figs. but it provides rapid and efficient preliminary meansfor clamping a printing plate or like work object in appropriateposition, coacting with final clamping means for exerting a highpressure on the work object, whereby extremely accurate and rapidprocessing may be realized.

It will be appreciated that, although the invention has been describedin detail with reference to one embodiment thereof, it may also bepracticed by substituting a wide variety of modifications or equivalentsfor the elements shown and described herein. All such modifications,including reversals of parts and the use of certain featuresindependently of the use of other features, are within the spirit andscope of the invention as defined in the appended claims.

Having thus described our invention, we claim:

1. Apparatus for bending and straightening a curved plate or the like,comprising a concave slab adapted to support said plate, readilyadjustable clamping means manually swingable to a position above andadjacent said concave slab against one end of said plate, screw clampmeans fixed on said concave slab effective upon the other end. of saidplate, and means to operate said screw clamp and thereby apply force tosaid other end of said plate, whereby the opposite ends of said plateare compressed toward one another and the body of said plate is expandedfor intimate contact under pressure with said concave slab.

2. Apparatus for modifying the surface shape of a concave platecomprising a concave slab having a fixed curvature substantially similarto the initial curvautre of said concave plate, tracks at one end ofsaid concave slab, a carriage mounted for movement along each of saidtracks, a ratchet member on each of said tracks, a pawl element on eachof said carriages and coacting with said ratchet member, a cross piecespanning said tracks and affixed to said carriages, said carriages andcross piece being movable along said tracks as a unit with the crosspiece immediately adjacent the curved face of said concave slab, Wherebysaid cross piece is adapted to abut the edge of one end of said concaveplate, and a plurality of screw clamps mounted on the other end of saidconcave slac, said screw clamps including clamping elements adapted toextend immediately adjacent the surface of said concave slab to abutagainst the edge of the other end of said concave plate.

3. An apparatus for holding a curved plate comprising a concave slab ofdetermined curvature, adjustable clamping means fixed to one edge ofsaid slab, substantially parallel tracks having a curvaturesubstantially equal to that of said slab, said tracks being fixed to andextending beyond the opposite edge of said slab, and separate clampingmeans slidably supported on and spanning said tracks.

4. In a method of straightening a localized low spot on the printingsurface of a curved printing plate, the steps comprising placing saidcurved printing plate on a concave slab with the printing surfacedisposed adjacent said slab, said slab having a curvature in excess ofthe curvature of the plate whereby the plate bridges across the slab,compressing opposed ends of said plate toward one another therebyexpanding said printing surface with the exception of said low spotagainst said concave slab, deforming the face of said plate locally inthe area of said low spot toward said concave slab to bring the printedsurface at said low spot in uniform contact with the adjacent portion ofsaid slab, and continuously maintaining the compression of the opposedplate ends toward one another during the deformation step.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 173,729 Jameson Feb. 22, 1876 1,760,559 Klocke May 27, 19302,220,671 Blaetz Nov. 5, 1940 FOREIGN PATENTS Number Country Date280,978 Germany Dec. 3, 1914

